Devices that derive electrical power from external sources, such as utility power, typically include a circuit connection and a ground connection for connecting to the external power source. Such devices include, among other things, consumer appliances, industrial equipment, and computer equipment. The circuit connection in such devices generally includes two contact points across which the device is connected to complete the power circuit. The ground connection in the device is intended to be connected to a electrical ground. According to many international safety standards, the ground connection must also electrically connect the metal chassis of the device to electrical ground.
Several international standards define tests relating to the electrical interconnection and/or isolation of the circuit connection, the ground connection, and the metal chassis of an electrical device. Such test are referred to herein as electrical safety compliance tests. Two common electrical safety compliance tests are those generally referred to as the dielectric withstand test, and the ground continuity test. Electrical devices must typically pass such tests before being sold commercially.
The dielectric withstand test measures the isolation between the circuit connection and the ground connection at high voltages. To this end, a high voltage typically exceeding 1000 volts AC or DC is applied across the circuit connection and the ground connection of the device. The current is then measured. If the current exceeds a maximum allowable current threshold, the isolation between circuit and ground connection of the device is considered to be insufficient. If the isolation between the circuit and ground connection is insufficient, high voltages may propagate to the metal chassis during operation of the device, thereby creating a potential safety hazard.
The ground continuity test measures the resistance between the ground connection and the device chassis. The ground continuity test assures that the metal chassis will be electrically grounded during normal operation of the device. If a high resistance is detected, the chassis may not be properly grounded, thereby creating a potential shock hazard.
One problem associated with performing the dielectric withstand test and the ground continuity test is that many countries have unique test requirements. While the type of tests are generally the same from country to country, the specific test parameters vary. For example, the U.S. standards body, UL, defines two alternative dielectric withstand tests. One UL dielectric withstand test requires that a product be able to withstand application of 1500 volts AC for one minute. Another UL dielectric withstand test requires that a device be able to withstand application of 1725 volts DC for one second. By contrast, the United Kingdom standards body, BABT, requires that a device be able to withstand 2800 volts AC for one minute or 2125 volts DC for one second. Still other standards, such as the CSA standard of Canada, require devices to withstand other levels of voltage for particular time increments. Specific parameters associated with the ground continuity test also vary among the different nations' standards.
Accordingly, in a manufacturing environment where different products are intended for export to different countries, testing a product for electrical safety compliance requires a labor intensive procedure of obtaining the applicable international standard, obtaining the test parameters associated with the applicable international standard, and performing the test on the device using the appropriate test parameters. Moreover, the test data must be recorded and associated with the device under test. Such activities are not only labor intensive, but furthermore require highly skilled operators who are knowledgeable about the products, their international markets, and the standards of various countries.
To assist in carrying out dielectric withstand tests and ground continuity tests, a dielectric tester known as the VITREK 944i Dielectric Analyzer has been developed, which is available from Vitrek Corporation of San Diego, Calif. The VITREK 944i Dielectric Analyzer (hereinafter "Vitrek Analyzer") performs AC and DC dielectric tests, ground continuity tests and other tests, based on input test parameters.
To alleviate the need for providing test parameters for each operation of a test, the Vitrek Analyzer allows a user to store up to ninety-nine test programs. To perform a particular test, the operator may select the appropriate one of the stored test programs through the keypad on the Vitrek Analyzer.
The Vitrek Analyzer also includes the ability to communicate with external devices, such as a general purpose computer. As discussed in the Vitrek 944i Dielectric Analyzer Operating and Maintenance Manual (Vitrek Corporation, 1994) (hereinafter "Vitrek Manual"), which is incorporated herein by reference, the Vitrek Analyzer allows individual tests to be configured and executed through an external communication link. In particular, the Vitrek Manual teaches that individual single step tests may be configured at a general purpose computer and then communicated to the Vitrek Analyzer. The Vitrek Manual also teaches that the Vitrek Analyzer may communicate test results over the communication link to an external device, such as general purpose computer.
While the Vitrek Analyzer provides a valuable tool for performing electrical safety compliance tests, the Vitrek Analyzer nevertheless has shortcomings. First, the user interface capabilities of the Vitrek Analyzer are limited. In particular, the stored test programs may only be accessed through the Vitrek Analyzer keypad by their two digit number. Thus, for example, if an operator stores several test programs in the Vitrek Analyzer, the operator must memorize or record on paper which test standard is associated with each stored test's two digit identification number. Moreover, the test programs stored in the Vitrek Analyzer may not be accessed through the communication link, or in other words, by an external computer. Thus, if the test programs stored in the Vitrek Analyzer are to be accessed, they must be accessed through operator input at the front panel of the Vitrek Analyzer, which, as discussed above, has extremely limited user interface capabilities.
Moreover, the Vitrek Manual does not teach a fully automated test system that is capable of performing tests that conform to the various nations' electrical safety compliance standards in an intuitive and straightforward manner. There is a need, therefore, for a fully automated test system that performs one of a plurality of electrical safety compliance tests with reduced labor effort and knowledge than that required by conventional test systems, including those taught by the Vitrek Manual. There is a further need for such a fully automated test system that is menu-driven, thereby reducing the complexity of operation of the system. There is yet a further need for a system that automatically obtains tracking identification data associated with each test performed by the automated test system.
Another difficulty encountered in electrical safety compliance testing arises from the hazardous conditions that occur during such testing. In particular, dielectric withstand tests routine require application of AC or DC voltages well in excess of 1000 volts to the DUT. Such voltages can be extremely hazardous to human beings. Accordingly, safety precautions must be taken to avoid inadvertent contact with a DUT while a test is in progress. Such precautions may include isolating the DUT in a closed room or closed area. The use of a closed room or physically closed off area can undesirably limit the location options of the electrical safety compliance testing area within a manufacturing facility. Moreover, use of such extensive physical barriers can be inconvenient to relocate.
Another hazard associated with electrical safety compliance testing is the residual charge the remains on the DUT after a test has been completed or stopped. In particular, the high voltages applied during the dielectric withstand test can result in a high voltage charge that remains on the DUT for some time after application of the high voltage has ceased. To address this issue, many testing apparatus, including the Vitrek Analyzer, include the capability to discharge the DUT. However, such internal discharge capabilities of the Vitrek Analyzer are relatively slow, and permit hazardous charge levels to remain on the DUT for a significant amount of time after the test has been completed.
There is an additional need, therefore, for providing safety precautions in the high voltage testing environment of electrical safety compliance testing that provides a more expedient discharge operation after a test has stopped or has been completed.